1. Field of the Invention
The present invention relates to the field of retorting of oil shale, particularly by treatment with superheated water vapor.
2. Description of the Prior Art
Technology for producing oily matter from kerogenous shales is very old, and for over 100 years, methods of retorting have been widely investigated. The use of superheated steam or vapor phase water (VPW) as a retorting agent has also been widely advocated, for example: Wells, W. E., and Ruark, J. R., Pilot Plant Batch Retorting of Colorado Oil Shale, pp 9-11, RI 4874, USBM, May 1952, showed the the use of steam in the Royster retort increased the shale off-gas volume by a factor of 2, and also markedly increased the hydrogen content of the off-gas; Synthetic Liquid Fuels, Part II, Oil from Oil Shale, pp 45-49, RI 4943, USBM, January 1953, and pp 35-39, RI 5044, USBM, April 1954, using an entrained solids retort, reported data on the use of high-temperature steam (1000-1500.degree.F.) as the entraining agent; Gavin, M. J., and Desmond, J. S., Construction and Operation of the USBM Experimental Oil-Shale Plant 1925-1927, USBM Bulletin No. 315, reported on the U.S. Bureau of Mines Experimental oil shale plant at De Beque, Colo., mentioning the use of steam injection in the operation of the `Pumpherston retort` during its operation in 1925 through 1927; Peck discusses the distillation of oil shale under fluidizing conditions using steam in U.S. Pat. No. 2,449,615; Belser disclosed the use of steam as a means of in situ recovery in U.S. Pat. No. 2,725,939; Schulman, in U.S. Pat. No. 3,520,795, outlines the use of steam in a shaft kiln as a means of retorting oil shale. In this patent, he is restricted to the temperature range, 950.degree. to 1050.degree.F.; Beard claims a method of in situ recovery of oil shale using steam in the temperature range, 550.degree. to 850.degree.F., in U.S. Pat. No. 3,739,851; Papadopoulos and Ueber in U.S. Pat. No. 3,741,306 claim an in situ method of converting kerogen to shale oil using steam injection at 650.degree.F.; and Gifford in U.S. Pat. No. 3,577,338 claims a method for retorting using steam and oxygen. British patent specification No. 1,326,455 contacts oil shale at a temperature in the range of 750.degree.-1500.degree.F. and a pressure in the range of 300-1000 p.s.i.g. with from 0.01 to 0.6 tons of H.sub.2 O per ton of oil shale and with a hydrogen-rich gas.
The investigations detailed in this patent application have led to the discovery that the pressure range under which treatment of oil shale with superheated water vapor occurs is surprisingly critical and that, furthermore, there is a critical interrelationship between the pressure at which said contact occurs and the superficial gas velocity required for maximum recovery of organic values from the oil shale. None of the above references teaches the importance of these factors or of the interrelationship between them. The interrelationship is particularly surprising inasmuch as, under certain conditions, increasing pressure actually deters the production of maximum organic values with other variables remaining the same.